Snippet to change Booking Product font-size of Time in Product Page. WooCommerce Bookings And Appointments - https://www.pluginhive.com/product/woocommerce-booking-and-appointments/

functions.php

/**
 * Snippet to change Booking Product font-size of Time in Product Page.
 * Created at : 19 Dec 2018
 * Updated at : 19 Dec 2018
 * PluginHive Plugins : https://www.pluginhive.com/plugins/
 * Gist Link : https://gist.github.com/varun-pluginhive/78996c9a57e98cf319a9b0f9d44a1e6a
 */
add_action( 'woocommerce_after_single_product', function() {
		?>
		<script>
			jQuery(document).ajaxStop(function() {
				let font_size = "25px";										// Font Size
				jQuery(".ph_calendar_time").css( "font-size", font_size);
			});
		</script>
		<?php
});

Or Add below Style to Theme style.css

/* Change Bookings Time Font Size Here*/
.ph_calendar_time{
font-size:20px !important;
}